yes, the headliner should be glued on to the roof - originally there was some thin foam glued to the roof, and then the headliner glued to it. The foam breaks down after so many years and the headliner comes adrift. I think there are a few posts on this forum, discussing what glue to use and tips on how to get it alligned right first time around. I agree that it can seem like sunvisors aren't that necessary, but when the sun is right down at the horizon, shining in your eyes, I find them useful. They turn up on e-bay quite often and the vendors probably have used ones that are serviceable. There is also a nifty mod to them to stop them flopping down all the time (this may be why yours are missing), involving drilling and pinning - it is also detailed on this forum I think.